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post #1 of 6 (permalink) Old 01-21-2014, 03:37 PM Thread Starter
jcl
 
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engine build

New to the site and need some expertise. Restoring a 66 GTO/ engine long gone. Ran accross a deal on a pre built 73 400,was never ran. It is 30 over with flat top pistons, 7K3 heads with crower springs and 1.6 rollers. It has a crower 60244 cam. I want to run an offenhauser dual quad with 2 450 hollys, which I already have. Will be running a M20 muncie, not sure on the rear gear yet . Thinking I would like to keep in the low 3s-1. will see very little if any strip time. Wondering about the cam choice and how it will perform set up as mentioned. I was told its running 9-1 comp ratio. I have not pulled the heads which is another issue I would like some input on. I have a set of 670 heads but not sure if I should use them. Not sure about how far I can push the compression ratio and perform on pumped gas. Any input or thought would be appreasiated. Anyone running this cam now would like to here what you think about it
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post #2 of 6 (permalink) Old 01-21-2014, 05:24 PM
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7k3's have a factory nominal chamber size of 96 cc's. If everything else about the engine is factory nominal +0.030 (that's a big if because there's lots of room for variance in there), then that engine is right at 8.144:1 which is a little on the low side. However, running the 670's would put you up around 10.4:1 which (in my opinion) would be too high for pump gas. Plus, the 670's are closed chamber heads and as such, need quite a bit of ignition advance to work well - just what you DON'T want if you're already over the limit on compression.

If your engine has been zero decked it could be up around 8.5:1 (still low).

Don't worry about "pushing" compression ratio. The truth is, changing compression alone doesn't make much difference in power output. On a street engine, it's almost never "worth" trying to push one right to the edge. The small amount of power (and I'm talking 10 hp or less) is rarely worth all the associated headaches and risk of grenading the motor.

It's very important to actually measure your chambers, and everything else about that engine, before you start in on it. The heads may have already been milled some, the block may have already been zero decked ---- all of which will have an effect on actual compression ratio.

For example if those heads have been milled about .040-.045 or so and have chambers that are now 86 cc's, and the block zero decked, then it'll be at 9.150:1 which is a pretty good place to be with iron heads.

That Crower 60244 is a fairly rowdy cam for a 400 street engine. You may find it's borderline for running vacuum accessories like power brakes.

HOWEVER - let's say you were to swap out the rotating assembly, crank, rods, and pistons --- transform it into a 461 (4.25 stoke, +035 overbore) --- then with those heads and flattops you'd be at 9.1:1 (nominal deck) or 9.4:1 (zero deck), and I promise you'd have a huge smile on your face every time you stood on it Plus, the extra inches would make that cam a lot more streetable.

Bear

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post #3 of 6 (permalink) Old 01-22-2014, 12:11 PM Thread Starter
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Thanks Bear for the info.

I do want to pull the heads and verify what I have. It was supposenly decked. The cam and vacuum are a concern, but its all new. I want to give a try. Still up in the air on the heads. I will have to see whats been done and go from there.

anyone out there running 670 heads above 10:1 on pumped gas ?

jcl
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post #4 of 6 (permalink) Old 01-22-2014, 12:33 PM
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Quote:
Originally Posted by jcl View Post
anyone out there running 670 heads above 10:1 on pumped gas ?
Not for long....


Ok - honestly? Maybe so, but not much above 10:1, and then only if everything else about the engine is dead-nuts perfect and kept that way all the time. I mean fuel mixture, cooling system - everything. It can also depend on what's been done to the chambers, decks, which cam profile, how the cam was installed (intake centerline), ignition timing, and other things like transmission, gear ratio - even how and where the car is driven. This is NOT a simple matter of an overhaul and reassembly. Every single component has to be carefully thought out, selected, and matched in meticulous detail in order to have a prayer at making it live. Attempting something like this is most definitely living on the razor's edge.

And I promise you, for every ONE person you find who's able to run 670's above 10:1 (even above 9.5:1) on 93 octane (not 91) successfully, you'll find FIFTY or more who tried it and completely ruined their engine, and in short order. All for what, less than 10 HP? Not for me.

But, it's up to you to decide "if you feel lucky" and if you're willing to spend the cash, put in the work, and take the risk.

Bear

p.s. --- You'll spend as much if not more on building that engine with 670's and making it live, with perhaps a 15% chance at success - than you would on turning it into a 461 that will run forever on pump gas with no worries, and will eat that 400 ALIVE on power. You pick

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post #5 of 6 (permalink) Old 01-22-2014, 04:13 PM Thread Starter
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Thanks again Bear

Not realy leaning toward the 670s just curious to what others had tried. Was hoping to here everybodys doing it and liking it, but was expecting the responce I got.

This thing could already be built close to 9-1 as I was told and you mentioned earlier. I will see once I pull the heads. I want to try and get as much out of the 7k3s as I can since the cam wants a higher compression, and see what she does. Hey I might like it. If not, out she comes back on the stand

Jcl

Last edited by jcl; 01-22-2014 at 04:35 PM.
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post #6 of 6 (permalink) Old 01-22-2014, 05:10 PM
 
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I'd prefer the 461 as well. I had 670's with more than 10:1... the important word is "had".
It will cause trouble, depending on fuel quality, cooling, ignition timing.. but you'll never be able to use the engines power with that combination and you risk a fatal damage (pistons killed by detonation...)
More cui's = more fun Stay at or below 9.5 with iron heads and you'll be able to enjoy it a long time.
If you want a radical cam that needs compression you might want to use aluminium heads.
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